The present invention relates generally to gas turbine engines, and, more specifically, to fan blades therein.
The high bypass turbofan gas turbine engine is commonly used for powering aircraft in flight. The fan includes a row of fan blades mounted to the perimeter of a rotor disk and powered by a corresponding turbine which extracts energy from combustion gases generated in a core engine. The core engine typically includes an axi-symmetrical multi-stage centrifugal compressor which provides pressured air to a combustor wherein it is mixed with fuel and ignited for generating hot combustion gases which flow downstream through a high pressure turbine which powers the compressor, followed in turn by a low pressure turbine which powers the fan.
Engine propulsion thrust is typically increased by increasing diameter of the fan blades, which also necessarily increases their weight and stress during operation. Accordingly, larger fan blades require correspondingly high strength materials in order to accommodate the various aerodynamic and centrifugal stresses generated during operation for obtaining a suitable useful life.
A typical fan blade includes an airfoil and an integral dovetail at the root thereof which permits individual assembly and disassembly of the blades in corresponding dovetail slots in the fan rotor disk. The blade dovetail must therefore have sufficient strength for transferring the significant centrifugal loads from the rotating fan blades into the perimeter of the rotor disk within acceptable stress limits. The size and configuration of the airfoil is determined by the specific aerodynamic requirements of the fan and is limited by the availability of suitable high strength materials capable of withstanding the various stresses experienced during operation.
For example, titanium is a common high strength material used in fan blades, but is undesirably expensive. A solid titanium fan blade is most readily manufactured, yet has a correspondingly high weight which adds to the centrifugal loads generated during operation.
Hollow titanium fan blades are also known for reducing weight while maintaining strength, but correspondingly increase the complexity of blade manufacture and associated costs.
Another form of the titanium fan blade is the hybrid fan blade which is primarily solid titanium with weight reducing pockets formed therein which may be filled with a lightweight, nonstructural filler material to complete the aerodynamic profile of the blade.
The hollow titanium blade has minimum weight with suitable high strength yet is very expensive to manufacture. The hybrid titanium blade is less expensive to manufacture yet does not enjoy the greater weight reductions of the hollow titanium blade.
Accordingly, it is desired to provide an improved high strength, low weight fan blade at reduced cost.